1. Technical Field
The invention relates to a colored curable composition, a resist liquid, an ink for inkjet printing, a color filter, a method of producing a color filter, a solid-state image sensor, a liquid crystal display, an organic EL display, an image display device and a colorant compound.
2. Background Art
Demands for liquid crystal displays (LCDs), in particular for color liquid crystal displays, have been increasing in recent years as technologies in personal computers and, in particular, large-size liquid crystal displays advance. There are also demands for organic EL displays to become more popular out of requirements for further improved image quality. Meanwhile, demands for solid-state image sensors, such as CCD image sensors, have been remarkably increasing against the backdrop of growing popularity of digital cameras and mobile phones equipped with a camera.
Color filters are used as a key device for these displays and optical elements, and there are increasing demands for lower cost as well as for improved image quality. These color filters typically have a colored pattern of three primary colors of red (R), green (G) and blue (B), and divide light transmitting the color filter into the three primary colors in a display device or a solid-state image sensor.
Colorants used in color filters need to have the following characteristics in common.
Specifically, these colorants are required to exhibit favorable spectroscopic characteristics in terms of color reproducibility; suppressed optical disorder such as light scattering that causes decrease in contrast of a liquid crystal display or unevenness in optical density that causes color irregularity or roughness of a solid-state image sensor; fastness under environmental conditions in which the color filter is used, such as heat fastness, light fastness or moisture fastness; a large molar light absorption constant that enables formation of a thin film; and the like.
A pigment dispersion method is employed as a method of producing a color filter as mentioned above. In this method, since a colored curable composition in which a pigment is dispersed in various kinds of curable compositions is used for preparing a color filter by photolithography or ink jetting, the obtained color filter is stable with respect to light or heat.
In a method of employing photolithography, colored pixels are obtained by applying a radiation-sensitive composition to a substrate by using a spin coater, a roll coater or the like, drying the same to form a film, and developing this film by performing pattern exposure. A color filter can be produced by repeating these processes for a number of times of the colors used in the color filter. Photolithography has been widely used as a suitable method for producing large-sized high-definition color filters, and advantages of this method have been particularly remarkable in the field of producing solid-state image sensors that require even higher levels of resolution in these days.
In the process of producing a color filter for a solid-state image sensor, microscopic patterns are formed by exposing via a mask having a microscopic pattern, developing the same with an alkali solution such that the unexposed portion is dissolved therein. In this process, however, adjusting the solubility (developability) of the cured portion and the uncured portion may be difficult. In particular, when the colored curable composition has a low solubility with respect to an alkali developer, favorable patterns may not be formed due to a colorant remaining in the uncured portion. Therefore, there is need for a colored curable composition having small dependency on the concentration of alkali solution.
In recent years, further improvements in fineness of color filters for solid-state image sensor are desired. However, in conventional pigment dispersion methods, it is difficult to further improve fineness in view of occurrence of color irregularity due to coarse particles of pigment, or the like. Accordingly, it is getting more difficult to apply photolithography by a pigment dispersion method to applications such as solid-state image sensors in which fine patterns are desired. Further, in the field of liquid crystal displays, there are problems in color filters produced by photolithography employing a pigment dispersion method, such as decrease in contrast due to light scattering caused by pigment particles or increase in haze, even though light fastness and heat fastness are favorable.
Moreover, in the technique of photolithography, since a series of processes including application of a radiation-sensitive composition, drying, performing pattern exposure and development need to be repeated for a number of times of colors, problems such as high costs or reduction in yield rate may arise. In particular, as demands for lower prices for expensive color liquid crystal displays increase, demands for lower prices for color filters, which occupies a large portion of the total cost, is increasing. Accordingly, a method of producing a color filter at higher productivity has been increasingly desired.
In view of these circumstances, as a method of producing a color filter that solves the problems in photolithography as mentioned above, a method of forming a color layer (color pixels) by depositing color ink by an inkjet method is proposed (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 59-75205 and 2004-339332).
An inkjet method is a recording method of forming characters or images by discharging ink droplets directly to a recording medium from extremely fine nozzles, and depositing the ink to the recording medium. This method has such advantages in that large-size color filters can be produced at high productivity, noises are low, operation suitability is favorable, and the like. In the production of a color filter by an inkjet method, an ink for inkjet printing produced by a pigment dispersion method is used. As an ink for inkjet printing produced by a pigment dispersion method is used, an ink for inkjet printing for a color filter is proposed, in which a binder component, a pigment, and a solvent having a boiling point of from 180° C. to 260° C. and a vapor pressure of 1.5 mmHg or less are contained (for example, see JP-A No. 2002-201387).
When an ink for inkjet printing produced by a pigment dispersion method is used for producing color filters, there is demand for improving discharge stability in order to deal with frequent occurrence of nozzle clogging caused by coagulation of pigment in the ink. Further, recoverability of an ink discharge state by performing a discharge recovery operation, such as wiping or purging, tends to decrease due to the coagulated pigment. Moreover, misdirection of ink discharge may occur as a result of nozzle surfaces being scraped with the coagulated ink during wiping.
When a dye is used instead of a pigment dispersion method, achievement of high definition by solving problems of color irregularity and roughness, in the case of color filters for solid-state image sensors, and improvements in optical characteristics in terms of contrast and haze, in the case of color filters for organic EL displays, are expected. Moreover, when a dye is used in an inkjet method, discharge stability is generally high and it is expected that the ink discharge state can be more easily recovered by wiping or purging, even when nozzles are clogged due to increased ink viscosity or the like.
In view of the above circumstances, use of a dye as a colorant has been studied (for example, see JP-A No. 6-75375). However, use of a curable composition containing a dye raises new problems as described below.
(1) Light fastness and heat fastness of dyes are typically inferior to that of pigments. In particular, there is a problem in that optical characteristics of dyes may change due to high temperature at the time of forming an ITO (indium tin oxide) film commonly used in FPDs (flat panel displays) such as an electrode for liquid crystal displays (LCDs).
(2) Dyes tend to suppress radical polymerization reaction, which makes it difficult to design a colored curable composition in a system in which radical polymerization is used as a means of curing.
In particular, in the case of photolithography,
(3) Ordinary dyes have a low solubility with respect to an aqueous alkali solution or an organic solvent (hereinafter, also simply referred to as a solvent), which makes it difficult to obtain a curable composition having a desired spectrum.
(4) Dyes tend to interact with other components in the curable composition, which makes it difficult to adjust the solubility in a cured portion and the solubility in an uncured portion (developability).
(5) When the molar light absorbance coefficient (ε) of a dye is low, a large amount of dye needs to be used. As a result, the amounts of other components such as a polymerizable compound (monomer), a binder or a photopolymerization initiator in the curable composition need to be reduced, whereby curability, heat fastness after curing, developability of (non)cured portion or the like of the composition may be lowered.
Due to these problems associated with dyes, it has been difficult to use dye for forming a colored pattern of a color filter having a small thickness and exhibits high definition and excellent fastness. Moreover, since color filters for a solid-state image sensor need to have a thickness of as thin as 1 μm or less, dye needs to be added in the curable composition in large amount, thereby exaggerating the aforementioned problems.
In connection with these problems, various methods including selecting the type of initiator or increasing the amount of initiator have been proposed (for examples, see JP-A No. 2005-316012). Further, a method of producing a color filter is proposed in which a colored pattern is exposed to light while heating a substrate after formation of the colored pattern in order to increase the polymerization rate by performing polymerization at an elevated exposure temperature (see, for example, Japanese Patent No. 3309514). Moreover, a method of producing a color filter is disclosed in which light exposure is performed between the development treatment and the heat treatment in order to suppress deformation of the color filter (see, for example, JP-A No. 2006-258916).
Focusing on favorable spectroscopic characteristics of color filters, colored curable compositions and colorant compounds in which a dipyrromethene dye is used have been studied (see, for example, JP-A No. 2008-292970).
Dye-containing colored compositions for a color filter has a problem in that, in addition to the aforementioned problems, when heat treatment is carried out after the formation of the color filter, color transfer tends to occur between adjacent pixels or between color filter layers when two or more of these are layered.
Moreover, since a large amount of dye needs to be added to the curable composition, relative contents of components that contribute to photolithographic properties are reduced. As a result, the pattern may be easily exfoliated in a region exposed to a low amount of light due to decreased sensitivity, or cause defective pattern formation, such as failure to achieve desired shape or color density due to deformation due to heat or elusion during development.
JP-A No. 2008-292970 discloses spectroscopic characteristics derived from light absorbance characteristics that are unique to dipyrromethene dyes, but does not discuss problems such as color transfer or defective pattern formation.
In view of the above circumstances, a first aspect of the invention provides a colored curable composition, a resist liquid and ink for inkjet printing that form a cured film that exhibits excellent color purity, a high light absorbance coefficient that enables formation of a thin film, and excellent robustness and pattern formation properties.
A second aspect of the invention provides a color filter that exhibits excellent color purity, fastness and pattern formation properties, as well as suppressed color transfer, an image device, a solid-state image device, a liquid crystal display, an organic EL display and an image display device.
A third aspect of the invention provides a method of producing a color filter that exhibits excellent color purity, fastness and pattern formation properties, as well as suppressed color transfer.
A fourth aspect of the invention provides a colorant that exhibits excellent absorbance characteristics, a high molar light absorbance coefficient, and as necessary, excellent developability.
The present inventors have studied various kinds of colorants and, as a result, found that a dipyrromethene dye compound having a specific structure in which a polymerizable group and a carboxyl group are introduced in the same molecule exhibits a favorable color hue and a high light absorbance coefficient, and excellent solubility with respect to an organic solvent. Moreover, the present inventors have found that a cured film formed by a colored curable composition containing this compound exhibits excellent fastness, suppressed color transfer and excellent pattern formation properties (exhibits a low dependency on the concentration of alkali developer).
As mentioned above, it is widely known that dyes tend to suppress radical polymerization reaction. Accordingly, little has been known concerning dipyrromethene dyes in which a polymerizable group is introduced in order to suppress color transfer, much less dipyrromethene dyes in which a carboxyl group is also introduced in order to achieve excellent pattern formation properties.
The dipyrromethene dye compounds according to the invention is a compound having a chelate structure. Although JP-A No. 2008-292970 discloses a compound having a dipyrromethene dye skeleton, this literature does not suggest introducing a specific substituent in a dipyrromethene dye in order to acquire properties required by a colored curable composition for forming a color filter at even higher definition (such as sufficient solubility with respect to an organic solvent, light fastness, heat fastness, temporal stability, solvent resistance after curing, color hue and transmission properties; in particular, pattern formation properties and color transfer when the dye is used for a resist), also in view of adverse effects against the stability of a chelate complex.